1. conditii
2x-1>0 deci x>1/2
2x>0 deci x>0
adica in intersectie x>1/2
acum 2x-1=(2x)^2
2x-1=4x^2
4x^2-2x+1=0
a=4
b=-2
c=1
delta 4-4*4=4-16=-12
nu avem radacini
2. AC=b=6
cos B=4/5 deci sin B^2=1-(4/5)^2=1-16/25=9/25
sin B=3/5
b/sin B=2R
6:9/25=2R
6*25/9=2R
2*25/3=2R
impartim la 2
R=25/3
